Precision alignment of an optical beam through optical devices and systems may pose a variety of challenges. Devices may contain multiple optical elements, each having an associated alignment error that must be corrected. For instance, in optical multiplexing, a number of beams from different sources may need to be aligned with the tip of an optical fiber and each beam path may have different alignment error due to inaccuracies inherent in the fabrication and placement of optical components used in the device. One approach to alignment involves individually aligning the beam source and target, as well as each optical component, in multiple dimensions as they are placed. Manipulating multiple interdependent components may be complex and time consuming, and may be difficult due to the size and configuration of the system. In addition, aligning the source or target can be difficult, since it may be electrically powered and have unique mounting or monitoring requirements. Also, the source or target may be the largest element and allowing for movement during alignment may increase the form factor of the entire device.
One example of an optical system requiring alignment is an optical network carrying multiple channels of information on an optical fiber. The information on each channel may be carried in an optical signal within a defined range of wavelengths that can be separated from the other channels. Wavelength division multiplexing (WDM) may be used to add a channel to the fiber or to combine and add a number of channels to the fiber. Wavelength division demultiplexing (WDDM) may be used to separate channels from the fiber.
One approach for WDDM is to use dispersion to separate the channels in an optical signal. However, it may be difficult to align the multiple dispersed channels with target fibers or other optical components intended to receive the separate channels. Among other things, temperature changes may cause thermal expansion or contraction of components that result in alignment error. Moreover, a long beam path may be required to achieve sufficient physical separation of the channels, which exacerbates alignment errors and may place limitations on the minimum size for the system.
Another approach involves using wavelength filters to separate individual channels from the incoming signal. In order to provide alignment, the signals may be carried to and from the filters by optical fibers coupled to the filters. However, a series of fiber loops may be required to route the signals to and from the filters, which can place limitations on the minimum size of the system. For instance, a WDDM may interface with a plurality of receive optical assemblies (ROSAs) which use a standard form factor, such as a GigaBaud Interface Converter (GBIC) form factor.
The GBIC specification was developed by a group of electronic manufacturers in order to arrive at a standard form factor transceiver module for use with a wide variety of serial transmission media and connectors. The specification defines the electronic, electrical, and physical interface of a removable serial transceiver module designed to operate at Gigabaud speeds. A GBIC provides a pluggable communication module which may be inserted and removed from a host or switch chassis without powering off the receiving socket. The GBIC form factor defines a module housing which includes a first electrical connector for connecting the module to a host device or chassis. This first electrical connector mates with a standard socket, which provides the interface between the host device printed circuit board and the module. The GBIC module itself is designed to slide into a mounting slot formed within the chassis of a host device.
Each GBIC may be coupled to an optical fiber loop that feeds into a filter. The fiber loops and other components may be included in a housing with a form factor much larger than the GBIC. Accordingly, one possible design for a 4-to-1 WDDM system would use four GBICs (one for receiving each channel) and a separate housing for the WDDM. In many applications, however, it may be desirable to provide a much more compact design, such as a WDM or WDDM that can be configured to fit within a single GBIC or smaller form factor.
Accordingly, there exists a need for improved methods and systems for routing and aligning beams and optical elements in an optical device, such as a WDM, WDDM or other optical device.